Various types of respiratory devices are well-known in the art, and the present invention deals with that class of devices generally referred to as either resuscitators and/or ventilators, depending upon their primary intended usage. As used in this application, a resuscitator is defined as an apparatus utilized for initiating respiration in a person whose breathing has stopped. Similarly, a ventilator is defined as a positive pressure apparatus, other than a resuscitator, utilized to assist in pulmonary ventilation. Most types of known prior art have been developed for use in hospitals and are adapted to be powered by electrical current received from the hospital, and are also adapted to utilize the hospital oxygen supply system.
While some portable resuscitators have been known in the past, these devices typically used bottled oxygen, which has an adverse weight to oxygen supply ratio. In addition, such devices which rely on bottled oxygen typically have a relatively short shelf life when compared to devices which relay on chemical oxygen generators. Therefore, it is desirable that a portable resuscitator be developed that has an acceptable weight to oxygen supply ratio and a relatively long shelf life.
Known portable resuscitators have operated only in a timed cycle mode wherein a volume of an air oxygen mixture is forced into a patient's lungs for a period of time and then the air oxygen mixture is permitted to expire for another period of time, the periods of time being selected to approximate a normal breathing cycle. Known portable ventilators could be operated in a demand mode wherein each inspiratory phase of ventilation is triggered by the inspiratory effect of the patient's breathing. Demand mode ventilators are not suitable for use as resuscitators, as the patient is incapable of triggering their operation. Similarly, timed cycle resuscitators are not desirable for use as ventilators or with patients who start breathing on their own, as a mismatch of the breathing cycle to the physiological needs of the patient could be traumatic. Therefore, it is desirable that a portable unit be developed which can operate either as a ventilator or a resuscitator, such a portable unit normally operating in a timed cycle mode, the timed cycle being capable of being overridden by a patient's inspiratory or expiratory efforts.